The invention relates to the automated translation of natural languages, and in particular to translation between English and Japanese.
Researchers have proposed various schemes for the machine-based translation of natural language. Typically, the apparatus used for translation includes a computer, which receives input in one language, and performs operations on the received input to supply output in another language. This type of translation has been an inexact one, and the resulting output usually requires editing by a skilled operator. To assist in this editing process, some translation systems include built-in editing facilities. One approach used in these systems has been to make alternate translations for individual words available to the operator. Another approach has been to provide a series of preferred alternate sentence translations and to permit the operator to choose the preferred one.
The translation operation generally includes a structural conversion operation. The objective of structural conversion is to transform a given parse tree (i.e., a syntactic structure tree) of the source language sentence to the corresponding tree in the target language. Grammar-rule-based structural conversion and template-to-template structural conversion have been tried. In grammar-rule-based structural conversion, the domain of structural conversion is limited to the domain of grammar rules that have been used to obtain the source-language parse tree (i.e., to a set of nodes that are immediate daughters of a given node). For example, given ##STR1## and: ##STR2## each source-language parse tree that involves application of the rule is structurally converted in such a way that the order of the verb and the object is reversed (note that in Japanese, the verb appears to the right of its object). This method is very efficient in that it is easy to find out where the specified conversion applies--it applies exactly at the location where the rule has been used to obtain the source language parse tree. On the other hand, it can be a weak conversion mechanism in that its domain, as specified above, may be extremely limited, and in that natural language may require conversion rules that straddle over nodes that are not siblings.
In template-to-template structural conversion, structural conversion is specified in terms of I/O templates or subtrees. If a given input template matches a given structure tree, that portion of the structure tree that is matched by the template is changed as specified by the corresponding output template. This is a very powerful conversion mechanism, but it can be costly in that it can take time to find out if a given input template matches any portion of a given structure tree.